Question: Simplify the following expression: $q = \dfrac{1}{8r} - \dfrac{1}{6r}$
Explanation: In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $8r$ and $6r$ $\lcm(8r, 6r) = 24r$ $ q = \dfrac{3}{3} \cdot \dfrac{1}{8r} - \dfrac{4}{4} \cdot \dfrac{1}{6r} $ $q = \dfrac{3}{24r} - \dfrac{4}{24r}$ $q = \dfrac{3 -4}{24r}$ $q = \dfrac{-1}{24r}$